Process for improving the elongation of grain refined copper base alloys

ABSTRACT

A PROCESS FOR IMPROVING THE ELONGATION OF COPPER BASE ALLOYS BY CONTROLLED GRAIN COARSENING. COPPER BASE ALLOYS CONTAINING FROM ABOUT 2 TO ABOUT 9.5% ALUMINUM, LESS THAN 1% ZINC,AND A GRAIN REFINING ELEMENT SUCH AS IRON, CHROMIUM, ZIRCONIUM, OR COBALT ARE SUBJECTED TO FINAL COLD REDUCTION OF FROM ABOUT 8% TO ABOUT 22% AND A FINAL ANNEAL OF FROM ABOUT 550 TO ABOUT 715* C. ALTERNATIVELY, THE ALLOY CAN BE SUBJECTED TO A SEQUENCE OF DECREASING REDUCTIONS INTERSPREAD WITH HIGH TEMPERATURE ANNEALS, FOLLOWED BY THE ABOVE FINAL REDUCTION AND ANNEAL.

United States Patent 6 3,788,902 PROCESS FOR IMPROVING THE ELONGATION OFGRAIN REFINED COPPER BASE ALLOYS Eugene Shapiro, Hamden, Jacob Crane,Woodbridge, and George H. Eichelman, Jr., Cheshire, Conn., assignors toOlin Corporation, New Haven, Conn. No Drawing. Filed Nov. 24, 1972, Ser.No. 309,345 Int. Cl. C22f I/08 U.S. Cl. 14811.5 R

ABSTRACT OF THE DISCLOSURE A process for improving the elongation ofcopper base alloys by controlled grain coarsening. Copper base alloyscontaining from about 2 to about 9.5% aluminum, less than 1% zinc, and agrain refining element such as iron, chromium, zirconium, or cobalt aresubjected to a final cold reduction of from about 8% to about 22% and afinal anneal of from about 550 to about 715 C. Alternatively, the alloycan be subjected to a sequence of decreasing reductions interspersedwith high temperature anneals, followed by the above final reduction andanneal.

BACKGROUND OF THE INVENTION It is common practice to add grain refinersto various solid solution, single-phase alloys for the purpose ofmaintaining a fine grain material during processing from the originalcast material to the final wrought condition. The grain refiner may beadded to improved processing and/ or to improve properties. In mostcases, the grain refiner serves to maintain uniform properties over acompositional range and over a range of processing conditions. In manycases, such as for copper base alloys containing aluminum and a grainrefining element such as cobalt, the grain refiners are not completelystable over the full range of temperatures :up to the melting point ofthe alloys because of decomposition or varying solubility.

Copper base alloys containing grain refiners maintain a fine grain sizeover a range of commercially suitable annealing temperatures and over arange of commercially acceptable solute concentrations. These alloysmaintain a relatively small variation in mechanical properties overthese temperature and composition ranges. This, of course, is a verydesirable feature commercially. It does, however, cause certainrestrictions in the normally available ductility of the alloy. Incontrast thereto, as a solid solution, single-phase alloy without grainrefiners is heat treated to higher annealing temperatures, the grainsize and the ductility of the alloy increase and the strength decreases.

It is common practice to anneal at the highest temperature consistentwith strength requirements to obtain material which requires unusuallyhigh ductility in forming operations such as stretch forming. Theannealing temperature is further limited for fabricating parts whichrequire a highly polished surface in that above a certain grain size, anorange peel condition occurs during fabrication which detracts from theappearance of the polished surface.

It is an undesirable feature of many grain refined cop per base alloysthat any attempt to coarsen the grain size above the stable levelimposed by the grain refining addition results in an uncontrolled mixedgrain size consisting of very small and abnormally large grains. Thisirregular grain growth is caused by factors such as secondaryrecrystallization which are a direct result of the effect of the secondphase particles on the matrix during cold working and subsequentannealing. Material subjected to irregular grain growth is not suitablefor fabrication into parts re- 15 Claims Patented Jan. 29, 1974 quiringsmooth surfaces for bufling and electroplating and causes nonuniformityof mechanical propertles.

SUMMARY OF INVENTION In accordance with this invention, a process hasbeen developed which permits certain grain refined copper base alloys toachieve uniform ductility with a controlled grain size. The processcomprises a final cold reduction of annealed metal of from about 8 to 22percent, followed by a high temperature anneal or a sequence ofdecreasing cold reductions interspersed with relatively high temperatureanneals. The process in accordance with this invention is particularlyapplicable to copper base alloys containing from about 2 to about 9.5percent aluminum, less than about 1 percent zinc, and a grain refiningelement selected from the group consisting of iron .001% to 5.0%,chromium .001% to 1%, zirconium 001% to 1.0%, co balt 001% to 5.0%, andmixtures of these grain refining elements. Preferably, the aforenotedalloys also contain from about .001 to about 3 silicon.

The alloys processed in accordance with this invention provide markedlyimproved elongation with a suitably small grain size.

Therefore, it is an object of this invention to provide a process forimproving the ductility of grain refined copper base alloys withoutsubjecting them to irregular grain growth.

It is a further object of this invention to provide a proc-' DETAILEDDESCRIPTION In accordance with this invention, a process has beendeveloped which permits certain grain refined copper base alloys toachieve improved ductility with a uniformly coarsened grain size.

The process is particularly applicable to copper base alloys containingfrom about 2 to about 9.5% aluminum, less than 1% zinc, and a grainrefining element selected from the group containing iron .001 to 5.0%,chromium .001 to 1%, zirconium .001 to 1.0%, cobalt .001 to 5.0%, andmixtures of these elements and the balance copper. Preferably, the alloyalso contains from about .001 to about 3% silicon, and the aluminumrange is from about 2 to about 5%. It has been found that the processingof this invention is particularly applicable to CDA Alloy 638 containing2.5% to 3.1% aluminum, 1.5% to 2.1% silicon, 0.25% to 0.55% cobalt, andthe balance copper.

It is desirable in accordance with this invention to provide theaforenoted copper base alloys in the wrought condition with improvedductility, as, for example, at least 40% elongation for CDA Alloy 638,without their being subject to irregular grain growth.

In accordance with one embodiment of this invention, an alloy within theaforenoted ranges of composition is provided in the annealed condition,the alloy having been annealed at a temperature of less than 600 C. Theannealed alloy is subjected to a final cold reduction of from about 8%to about 22%, and preferably from about 10% to about 20%. The coldworked alloy is then subjected to a final anneal at a temperature offrom about 550 C. to about 715 C., and preferably from about 650 C. toabout 700 C.

It has been found that the elongation increases with increasingtemperatures in the final annealing step. The

aforenoted process yields a wrought alloy having a substantially uniformgrain size of less than 0.025 millimeters, an ultimate tensile strengthof at least 70 k.s.i., a 0.2% yield strength of at least 30 k.s.i., andan elongation of at least 40%. It has been possible to achieve with CDAAlloy 638 elongations as high as about 45% with an ultimate tensilestrength of about 74 k.s.i., and a 0.2% yield strength of about 40k.s.i.

In accordance with preferred embodiments of this invention, the processis carried out in a sequence of cold reductions interspersed withrelatively high temperature anneals.

In accordance with one preferred embodiment, an alloy within theaforenoted ranges of composition is subjected to an amount of cold worksuflicient for it to recrystallize at less than about 600 C. Generally,this comprises cold reducing the alloy at least and preferably at least30%. The maximum amount of cold work performed is governed by the gagerequirements for the alloy. The cold worked alloy is then subjected toan intermediate anneal at a temperature of from about 400 to about 600C., and preferably from about 450 to about 575 C. The intermediateannealed alloy is then subjected to a final cold reduction of from about8% to about 22%, and preferably from about 10% to about 20%. The finallycold worked alloy is then subjected to a final anneal at a temperatureof from about 550 to about 715 C., and preferably from about 650 toabout 700 C.

As with the process of the preceding embodiment, elongation increaseswith the temperature of the final anneal. Similar properties areobtained as those set forth for the process of the previous embodiment.It has been found, however, that the intermediate annealing temperatureis in every sense critical in that temperatures exceeding about 600 C.result in irregular grain growth in the alloy, if the alloy haspreviously been subjected to a cold reduction of at least about 22%.

In accordance with a still further embodiment of the invention, an alloywithin the aforenoted ranges of composition is subjected to a coldreduction of at least 10%, and preferably at least 30%, depending ongage requirements; the cold worked alloy is then intermediate annealedat a temperature of from about 400 to about 600 C., and preferably at atemperature of from about 450 to about 575 C.

The annealed alloy is then subjected to a cold reduction of from about25 to about 40% and then to an intermediate anneal at a temperature offrom about 400 to about 600 C., and preferably at a temperature of about450 to about 575 C. The intermediate annealed alloy is then subjected toa final cold reduction of from about 8% to about 22%, and preferablyfrom about 10% to about 20%. The finally cold worked alloy is thensubjected to a final anneal at a temperature of from about 550 to about715 C., and preferably at a temperature from about 650 to about 700 C.This embodiment of the invention provides greater flexibility in meetinggage requirements in accordance with this invention, and should givemore uniform recrystallization of the alloy and more uniform properties.

As with the previous embodiment, the intermediate an- .nealingtemperatures are critical if the alloy has previously been subjected toa cold reduction of at least 22%.

In all of the embodiments discussed in accordance with this invention,the final cold working and final annealing steps are critical to obtaina wrought alloy having improvide elongation without irregular graingrowth. The processes of this invention provide uniform grain coarseningand substantially uniform grain sizes of less than .025 millimeters. Ifthe upper limit for the final annealing temperature is exceeded inaccordance with this invention, the alloy is subject to irregular graingrowth. This is similarly the case with respect to the final coldWorking step, since a reduction of greater than 22% will produce theonset of irregular grain growth.

While the invention has been described with respect to specificembodiments, it is possible that other processing steps can be performedin addition to the processing of this invention so long as thelimitations on the intermediate annealing temperature and final coldworking and final annealing are adhered to.

The times at temperature and the heat up and cool down rates for theannealing steps of this invention are not critical and may be set asdesired in accordance with conventional practice for these types ofalloys.

The following discussion is believed to set forth the mechanisms whichgovern the critical nature of the processing of this invention. Themechanisms set forth are not meant to be limitative of the invention.

In alloys of low stacking fault energy containing dispersed second phaseparticles, e.g. Alloy 638, a 50% cold reduction results in a strong{ll0} ll2 deformation texture or preferred orientation. When Alloy 638is recrystallized at 500 to 600 C., it contains newly formedrecrystallized strain-free grains of very small size. The strong pinningeffect of the CoSi dispersed second phase insures retention of finegrains. At higher annealing temperatures above 600 C., the pinning forcediminishes as the CoSi agglomerates and/ or resolutionizes. Under theseconditions, newly recrystallized grains which have a {ll0} ll2 annealedtexture or preferred orientation grow preferentially into the l-10} 112texture of the still deformed regions. Preferential grain growthcontinues even after recrystallization, since the larger grains ofpreferred orientation have more rapid growth rates than their smallerneighbors of different orientations. This preferential grain growthconstitutes the undesired irregular grain growth and yields a duplexmicrostructure.

The {ll0} ll2 type texture has been found to be the stable end texturein cold rolled, low stacking fault energy alloys, such as Alloy 638.Irregular grain growth results in a {ll0} ll2 type annealed texture. Itis believed that the development of the irregular grain growth and the112 annealed texture is related to the presence of a critical amount of{ll0} ll2 deformation texture before the final recrystallization anneal.

The terms texture or preferred orientation as used in this applicationrefer to the planes of the grains which are parallel to the stripsurface.

It has been found in accordance with this invention that if the finalcold working step is maintained within the aforenoted ranges ofreduction, the amount of {110} 1l2 deformation texture is maintainedbelow the critical level so that irregular grain growth will not occurduring final annealing within the specified temperature ranges.Therefore, the processes of this invention provide uniform graincoarsening without duplex or irregular grain growth.

The processes of the invention will now be illustrated by reference tospecific examples.

In the examples in all the final anneals and intermediate lalnneals, thesamples were held at temperature for one our.

The annealing temperature, as the term is employed in this application,refers to the temperature of the metal rather than the furnacetemperature.

Example I Samples of CDA Alloy 638 having a composition of 1.98%silicon, 2.5% aluminum, 0.42% cobalt, and the balance copper wereprepared by commercial means to 0.090 inch gage. The samples were thenprocessed in accordance with the process sequences in the tablefollowing. The mechanical properties and grain sizes for the samples areshown in the table.

Processing sequences A GR 507, Ann. 575 (l/CR 507 Ann. 575 C B 0325iAnne. 575 CJCR 30 Ann. 575 0.] CR 15%,

C CR 45%, Ann. 575 0 /CR 30%, Ann. 575 C./CR 15%,

Ann. 700 C N own-G R=cold roll; Ann. =anneal.

This example shows that a range of elogation and strength properties anduniform grain coarsening which results in a suitably small grain sizecan be obtained by the processes of this invention.

Process Sequence A corresponds to conventional processing for this alloyand is not in accordance with the process of this invention. It ispresented by way of comparison.

Processing Sequences B and C illustrate that if the final cold workingstep is kept within the range of reduction in accordance with thisinvention, uniform grain coarsening and marked improvements inelongation can be obtained upon final annealing over a range ofannealing temperatures.

Example II Samples of CDA Alloy 638 having a composition of 1.98%silicon, 2.5% aluminum, 0.42% cobalt, and the balance copper wereprepared by commercial means to 0.080 gage- The samples were givenvarying final cold reductions and were annealed at varying finalannealing temperatures. The resulting relationships are tabulated below.

Deformation, percent 0. 005 and 0. 030. 0. 060.

1 Duplex microstructure. t 9 Grain size after development of the hightemperature gram growth exture.

Samples of CDA Alloy 638 having a composition of 1.98% silicon, 2.5aluminum, 0.42% cobalt, and the balance copper were prepared bycommercial means to 0.090 inch gage. The samples were processed inaccordance with the following sequence, wherein the intermediateannealing temperature was varied. The results are tabulated below.

PROCESS SEQUENCE OR 45%, Ann. 575 0.; CR 30%, I. Ann.; CR 15%, Ann. 700C.

UIS, 0.2% Ye, E, Grain I. ann., C. k.s.i. k.s.i. percent size, mm.

' Mostly 0.0050010 mm. grains, but 0.030 mm. grains were observedindicating exaggerated grain growth.

This example clearl illustrates the critical nature of the intermediateannealing temperature. The example shows that if the intermediateannealing temperature after a cold reduction of at least about 22%exceeds about 600 C., one can expect the onset of exaggerated graingrowth.

+Samp1es in annealed condition anealed at less than 600 C.

Grain UTS, 0.2% YS, size,

k.s.i. k.s.i. percent mm.

Example IV Temperature, C.

Percent cold work:

15 U D U D D D D D 1 An almost entirely uniform structure, 1 or 2isolated coarse grains.

Norn.-D=Duplex grain structure; U=Uniform grain structure These resultsindicate that final reductions within the ranges of this invention willresult in a uniform grain structure, whereas reductions outside themange of this invention, as, for example 25%, will result in irregulargrain growth and a consequent duplex grain structure. The resultsfurther indicate that for final anneals at temperatures outside therange of the instant invention, namely above 715 0., a uniform grainstructure cannot be assured for any of the degrees of cold reductionshown.

The aforenoted examples illustrate clearly the criticalnature of theintermediate annealing temperature, the final cold reduction, and finalannealing temperature in accordance with the processes of thisinvention.

While the invention has been described with reference to a single finalcold reduction and anneal, it should be evident from the above that aseries of cold reductions and anneals within the ranges of the finalcold reduction and anneal could be employed Without subjecting the alloyto irregular grain growth. This invention, therefore, also covers such asequence of a plurality of reductions and anneals within the ranges ofthe final reduction and anneal.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:

1. A process for improving the elongation of copper base alloys bycontrolled grain coarsening comprising:

providing a copper base alloy containing from about 2 to about 9.5%aluminum, less than about 1% zinc, a grain refining element selectedfrom the group consisting of iron from about .001% to about 5.0%,chromium from about .001% to about 1%, zirconium from about 001% toabout 1.0%, cobalt from about .001% to about 5.0%, and mixtures of theseelements, and the balance copper, said alloy being in the annealedcondition;

+Samples in annealed condition anealed at less than 600 C.

subjecting said alloy to a final cold reduction of from about 8% toabout 22%; and

then final annealing said alloy at a temperature of from about 550 toabout 715 C.

2. A process as in claim 1 wherein said alloy further contains fromabout .001 to about 3% silicon, and wherein the aluminum content is fromabout 2 to about 3. A process according to claim 2 wherein said alloycontains 2.5 to 3.1% aluminum, 1.5% to 2.1% silicon, 0.25% to 0.55%cobalt, and the balance copper.

4. A process according to claim 3 wherein the final cold reduction isfrom about to about 20%.

5. A process according to claim 4 wherein the final annealingtemperature is from about 650 C. to about 700 C.

6. A process for improving the elongation of copper base alloys bycontrolled grain coarsening comprising:

(A) providing a copper base alloy containing from about 2 to about 9.5%aluminum, less than about 1% zinc, a grain refining element selectedfrom the group consisting of iron from about .001% to about 5.0%,chromium from about 001% to about 1%, zirconium from about 001% to about1.0%, cobalt from about .001% to about 5.0% and mixtures of theseelements, and the balance copper, said alloy being in the annealedcondition;

(B) cold reducing said alloy at least 10% so that it will recrystallizeat a temperature of less than about 600 C.;

(C) then intermediate annealing said alloy at a temperature of fromabout 400 to about 600 C.;

(D) then finally cold reducing said alloy from about 8% to about 22%;and

(B) then finally annealing said alloy at a temperature of from about 550to about 715 C.

7. A process as in claim 6 wherein said alloy further contains fromabout .001 to about 3% silicon, and wherein the aluminum content is fromabout 2 to about 5%.

8. A process according to claim 7 wherein said alloy contains 2.5% to3.1% aluminum, 1.5% to 2.1% silicon, 0.25 to 0.55 cobalt, and thebalance copper.

9. A process as in claim 8 wherein the cold reduction in Step Bcomprises at least 30% and the intermediate annealing temperature inStep C is from about 450 to about 575 C.

10. A process as in claim 9 wherein the final cold reduction of Step Dis from about 10% to about 20% and wherein the final annealingtemperature of Step E is from about 650 to about 700 C.

11. A process for improving the elongation of copper base alloys bycontrolled grain coarsening comprising: (A) providing a copper basealloy containing from about 2 to about 9.5% aluminum, less than about 1%zinc, a grain refining element selected from the group consisting ofiron from about .001% to about 5.0%, chromium from about .001% to about1%, zirconium from about .001% to about 1.0%, cobalt from about 001% toabout 5.0%, and mixtures of these elements, and the balance copper, saidalloy being in the annealed condition;

(B) cold reducing said alloy at least 10% so that it will recrystallizeat a temperature of less than about 600 C.;

(C) then intermediate annealing said alloy at a temperature of fromabout 400-to about 600 C.;

(D) then cold reducing said alloy from about 25 to about 40%;

(E) then intermediate annealing said alloy at a temperature of fromabout 400 to about 600 C.;

(F) then finally cold working the alloy from about 8% to about 22%; and

(G) then finally annealing said alloy from Step F at a temperature offrom about 550 to about 715 C.

12. A process as in claim 11 wherein said alloy further contains fromabout .001 to about 3% silicon, and where the aluminum content is fromabout 2 to about 5 13. A process according to claim 12 wherein saidalloy contains 2.5% to 3.1% aluminum, 1.5% to 2.1% silicon, 0.25 to 0.55cobalt, and the balance copper.

14. A process as in claim 13 wherein the cold reduction in Step B is atleast 30% and wherein the annealing temperatures in Step C and Step Eare from about 450' to about 575 C.

15. A process as in claim 14 wherein the cold reduction in Step E isfrom about 10% to about 20% and wherein the annealing temperature inStep F is from about 650 to about 700 C.

References Cited UNITED STATES PATENTS 2,210,672 8/1940 Kelly -1622,669,534 2/1954 Richardson 148-11.5 R 3,253,911 5/1966 Cairns 75-1623,475,227 10/1969 Caule et al 14811.5 R 3,656,945 4/1972 Eichelman, Jr.14811.5 R 3,725,056 4/1973 Ingerson 75162 WAYLAND W. STALLARD, PrimaryExaminer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3,7 ,9 Dated January 9, 197

Inventor(s) Eugene piro et a1.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In Column 1, line 31, the word "improved" should read ---improve---.

In Column 5, line 8; under the heading Grain Size, mm, -"0. 912'" shouldread -0 .012---;

In Column 5-, line 10, the word "elogation" should read --elongati onv vv Signed and sealed this 10th day of September 197A.

'(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents USCOMM-DC 60376-P69 FORM po-wso (10-69) I 11.5. GOVERNMENTPRINTING OFFICE: 1969 0-366-331

